The use of ophthalmic lenses for the correction of ametropia is well known. For example, multifocal lenses, such as progressive addition lenses (“PALs”) are used for the treatment of presbyopia. The progressive surface of a PAL provides far, intermediate, and near vision in a gradual, continuous progression of vertically increasing dioptric power from far to near focus, or top to bottom, of the lens.
PALs are appealing to the wearer because PALs are free of the visible ledges between the zones of differing dioptric power that are found in other multifocal lenses, such as bifocals and trifocals. However, an inherent disadvantage of PALs is the presence of unwanted astigmatism, or astigmatism that is undesirable and is introduced or caused by one or more of the lens' surfaces. Unwanted astigmatism can produce swim, image magnification, and motion effects for the lens wearer that disrupts the wearer's vision. In hard PAL lens designs, the unwanted astigmatism borders the lens channel and near vision zone. In soft designs, the unwanted astigmatism may extend into the distance zone. Generally, in both designs, the unwanted astigmatism at or near its approximate center reaches a maximum that corresponds approximately to the near vision dioptric power of the lens. A need exists for lens designs in which these localized maxima are reduced or substantially eliminated.